Electronic timer



March 6, 1956 Q MUN-r2, JR 2,737,602

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HEATER @wwf/WMM AGE/VT United States Patent O ELECTRONIC TIMER George Muntz, Jr., Levittown, N. Y. ApplicationApril 20, 1953, Serial No. 349,926 7 Claims. (Cl. 307-406) This invention relates to electrical timers and more specifically to such timers in which the timing interval can be automatically regulated.

In timer controlled, repeat cycle, electric heating operations, it is frequently desirable to produce the same amount of heat in each cycle. This is easy to accomplish if the line voltage remains constant. However, commercial power line voltage often varies over wide limits and as the heat produced by electric heating devices varies as the'square of the voltage, a 10% change in line voltage causes over 20% change in amount of heat.

It isv an object of the present invention to provide an el'licient electronic timer which produces a timing interval which is automatically regulated to compensate for heating Variations due to line voltage changes.

It is another object of the invention to provide such an automatic timer which can also produce uniform time intervals, if desired, despite such line voltage changes.

These and related objects are attained by providing, in an exemplary embodiment of the invention, an electronic timer in which the time a condenser takes to discharge through a resistance is varied in inverse manner to the change in line voltage. One way this can be accomplishedv is to connect one side of the condenser to ground and allow the potential of the other side to change from a constant negative value during idle periods to a positive value after the timing period by connecting the ungrounded side through a high resistance to a source of positive voltage which varies with the line voltage. As the condenser discharges through a resistance, the potential of its ungrounded side passes through zero. Substantially at this point, it triggers a tube, which upon becoming conducting, causes the circuit supplying voltage to the condenser to become non-active, thus ending the timing period. The value of the positive voltage applied determines the timing period and this value, of course, changes with line voltage variations. It is obvious that other ways of applying a voltage varying with the line voltage to the condenser can be used n place of the one just described. If it is desired to have a constant timing period regardless of line voltage changes, both the negativeidle period voltage on the condenser and the positive timing period voltage applied thereto are allowed to vary with the line voltage.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which:

Fig. 1 is a circuit diagram of a timer circuit in accordance with the invention;

Fig. 2 is a graphical representation to aid in explaining the operation of the invention; and

Fig. 3 shows how the timer can be connected to a utilization device.

Referring more specifically to the drawing, Fig. l shows, by way of example for purposes of illustration, a circuit diagram of a timer in accordance with the invention. The timing period is determined by the discharge period of a condenser 11. When the condenser voltage, as will be pointed out more fully below, reaches a certain value, the condition of a relay contact is changed and the timer period ends. During the timer period, contacts 28a and 28b, connected respectively to the terminals 12 and 13 of the timer 10 are connected together and line voltage from lines L1 and L2 (see Fig. 3) are applied through the timer 10 to a heater or other utilization device 15. During the olf periods, relay contacts 28b and 28e connected respectively to terminals 13 and 14 of the timer 10 are connected together and the line voltage is not applied to the device 15. (It it is desired to connect the device 15 to the lines L1 and L2 at all times except those determined by the timing period, terminals 13 and 14 would be used in the circuit of Fig. 3 instead of terminals 12 and 13.)

Returning now to the circuit of Fig. 1, power is applied to the timer 10 by means of terminals 16 and 17, assuming a line voltage of 240 volts. If the usual line voltage is other than 240 volts, the input lead 17 is made to an appropriate inner point of the input winding 18 of the transformer 19 which has a plurality of secondary windings 20, 21, and 22. The windings 21 and 22 are used to supply filament voltage to various tubes in the circuit. The secondary winding 20 is proportioned with respect to the primary winding 18 so that about 195 volts is applied to the anodes of the tubes V1 and V2 which are connected in well known manner as a full-wave rectifier. The output ofthe rectifier is filtered by the condenser 23 and applied across a resistance 24 and cold cathode, gas lled voltage regulator tube V4 in series. By way of example, 260 volts direct current is normally applied across elements 24 and V4 in series. Since the voltage across the tube V4 is held constant, al1 variations in voltage across the condenser 23 due to changes in line voltage appear across the resistor 24 and these changes are transmitted to the condenser 11 through the time range switch 37 and the resistor 29 or 36 selected thereby.

Also connected across the condenser 23 is a series circuit including a Stop switch 25 (normally closed), a Start switch 26 (normally open), a resistor 27, and the coil of relay 28. The relay has 28a, 28b and 28o already described and also contacts 28d and 28e. Contact 28d is normally open and is connected to short the terminals connected by the Start switch or button 26, thus making it unnecessary to keep the button 26 pushed down. Contact 28e is normally closed and when in this position applies a constant negative voltage on the ungrounded side of the condenser 11 from a setting of the potentiometer formed by resstances 30, 31 and 32 connected in series across the voltage regulator tube V4. Contacts 28b and 28C are, as mentioned above, adapted to connect terminals 13 and 14 together (the latter not connected to anything in the usual operation of the present invention) when the relay 28 is not operated and to contacts 28a and 28b connect terminals 12 and 13 together when the relay operates.

Connected across the resistance 24 (the voltage across which varies in accordance with changes in line voltage) is a series circuit including resistors 33 and 34 and the anode-cathode path of the normally non-conducting tube V3 which is preferably a high vacuum tube. The grid of this tube is connected to the ungrounded side of the condenser 11 whereby the tube can pass current when the negative bias thereon is removed by the change in charge on the condenser. The anode of the tube is connected back to the control grids of the two rectifier tubes V1 and V2 to cut oli:` these tubes when the tube V3 passes current. When the tube V3 changes from a cut-oilcondi` tion to conduction a voltage drop appears across the plate resistor 33. It will be noted that the positive end of resistor 33 s connected to the cathodes of tubes V1 and V2. ln this manner a negative bias voltage is provided to cut-oft tubes V1 and V2. This cut-off action is of short duration suflicient to allow relay 28 to drop out, opening contact 28d. In order that this action may be completed effectively the capacity of condenser 23 must be sutlicient to maintain the voltage drop across resistor 33 until the relay drops out. The discharge of condenser 23 also goes to the relay and does tend to keep it from dropping out immediately; however the circuit values are so arranged that the relay will dropout before the tubes Vl and V2 again become conducting. With a 50% drop in voltage the relay will drop out but the negative bias on V1 and V2 will still be enough to hold them cut-off.

The operation of the circuit shown in'Fig. l will now be described. The timer 1l) is connected as shown in Fig. 3 between Vthe line voltage connections L1 and L2 and the heater or other utilization device l5. Power is also applied to the rectifier V1-V2 through leads 16 and 17 and transformer 19. The Start switch 26 to commence the timing operation is then operated and direct current from theV rectifier Vl-VZ passes through the coil of the relay 28, locking in contact 28d, opening contact 28e, and closing contacts 28a and 2b which connect line Ll to the heater as shown in Fig. l. Prior to pushing the Start button 26, the ungrounded side of the condenser 1l (the upper one in Fig. l) has had a negative potential applied to it by means of the relay contact 23e and potentiometer 3%, 3l and 32. This negative potential is constant (though the value of it can be adjusted by varying the value of the resistor 3l or the setting of the resistor 30) because this potentiometer is connected across the voltage regulator tube V4 when the latter is connected as shown in Fig. l. This negative potential is represented by the value E2 in the graph of Fig. 2. VThe time setting is adjusted by changing the amount of negative charge. For example, a l() volt setting (curve No. l-the full line one-in Fig. 2), produces a time, for normal voltage, of about 70 seconds. A lesser voltage produces a smaller normal voltage timing period. A volt setting, for example, assuming otherwise the same conditions as for curve No. l, will produce a normal timing period of about 14 seconds. VAfter the Start button 26 is pushed and the relay Contact No. 2 opens, the negative potential from the potentiometer 3d, 3l, 32 is removed from the upper side of the condenser 1l and aV positive potential (E1 in the curves of Fig. 2) which is applied to this condenser through the time range switch 37 and the selected one of the resistors 29 and 36 gradually reduces the negative charge to zero and it allowed to continue would charge this capacitor with a positive potential. When the charge on it is reduced to Zero, that is, at the time at which the charge is changing from negative to positive, the tube V3 changes from a cut oft condition to a conducting one. This can be called the trigger time. The time that elapses between the pressing of the Start button 26 and the trigger time depends on the amount of negative charge originally on the condenser l1 and the value of the positive voltage connected through the switch 37 and the selected one of the resistors 29 and 36. This positive voltage will change with any change in line voltage and when it changes the time interval also changes. Thus curve No. 2 in Fig. 2

3. represents the condition when the line voltage is higher than normal and E1 varies proportionately. The time period has been reduced (to 57 seconds in Figs. 2, for example) to compensate for the change in voltage.

It desired, both Ei and E2 can be changed proportionately by moving the switch 38 to the left hand position in Fig. l to include the resistor 35 in series with the resistor 24. Curve No. 3 in Fig. 2 shows a condition where even though the line voltage is low, the period T remains the same as in curve No. l.

Examples (for illustration only and not by way of 1imi tation) of suitable circuit constants which can be used in the circuit of Fig. l are: Tubes V1 and V2, 2D2l; tube V3, 12AX7; condenserf 2l, 8 mfd.; resistor 24, 8.8

`kilohms; resistor 33, 50 kilohms; resistor 34, 5 kilohms;

resistor 29, l megohm; resistor 36, l0 megohms; resistor 3?, 15 kilohms; resistor 31, l kilohm; and resistor 32, 4 kilohms. Obviously, many changes in these circuit constants can be made without changing the invention.

It is clear that there are various other ways of altering the ratio of E1 to Ez and it is not intended to limit the invention to the one specifically described. Moreover, other changes will occur to those skilled in the art without departing from the spirit or scope of the invention.

What is claimed is:

l. A timer circuit comprising a condenser, means for connecting one terminal of said condenser to a point of iixed reference potential, means for connecting the other terminal of said condenser during idle periods of the timer to a source of Xed potential, means operative on starting the timing period for applying to said other terminal of the condenser through a resistance another potential which may vary in accordance with variations in the voltage ot the power line to which said timer circuit is adapted to be connected, and means actuated when said condenser charge reaches a predetermined point for changing a circuit condition ending the timing period.

2. The combination as in claim l in which said point of xed reference potential is ground, said source of xed potential is negative and said other potential is positive.

3. In combination, a condenser, means for grounding one side of said condenser, means for applying a xed potential of one sign to the other side of said condenser, means `for removing said fixed potential and for applying through a resistor a potential of the opposite sign to said ungrounded side of the condenser, and means operative when the potential of said ungrounded side passes through zero to cause a circuit change.

4. The combination as in claim 3 in which said potential of the opposite sign may vary with line voltage conditions.

5. An electric timer adapted to be used with a line voltage which may vary, comprising means for determining a timing period, and means for increasing said timing period as said line voltage decreases and for decreasing said timing period as said line voltage increases.

6. The combination as in claim 5 in which said rstmentioned means includes a condenser.

7. The combination of elements as in claim 5 in which said last-mentioned means is controlled by said line voltage.

No references cited. 

